Human Brain Anatomy PDF

## HERSENEN The brain consists of the cerebrum, the cerebellum and the brainstem. They are surrounded by three meninges that provide protection. The cerebrospinal fluid that is produced in the cavities of the brain, protects the brain and the spinal cord from shocks, provides transport of nutrients...

## HERSENEN The brain consists of the cerebrum, the cerebellum and the brainstem. They are surrounded by three meninges that provide protection. The cerebrospinal fluid that is produced in the cavities of the brain, protects the brain and the spinal cord from shocks, provides transport of nutrients and waste products and plays a role in maintaining the right temperature for these organs. The cerebrum and the cerebellum each consist of a left and a right half. They are connected in the middle by the corpus callosum. In the cerebral cortex (the outermost part) of the cerebrum and the cerebellum lies the gray matter. The cell bodies of interneurons lie here. Because the cerebral cortex is strongly folded, there are many folds and grooves. In the medulla (the innermost part) lies the white matter with axons of interneurons (see Figure 33). The white color is caused by the myelin sheaths which surround the axons. - **Afb. 33** Cross-section of the cerebrum. The brainstem is the part between the cerebrum and the spinal cord. The brainstem conducts impulses from the cerebrum and cerebellum to the spinal cord and vice versa. In the brainstem lie different centres that regulate important body functions, such as the heart rate, the diameter of blood vessels and the breathing rate. Cranial nerves from the brainstem also conduct impulses from receptors in the head and neck to the cerebrum and cerebellum and in the opposite direction to effectors. The lower part of the brainstem, where the brainstem transitions to the spinal cord, is called the medulla oblongata (see Figure 34). In the medulla oblongata, the nerve tracks cross each other. The impulses of the left half of the body are conducted to the right cerebral hemisphere and the impulses of the right half of the body to the left cerebral hemisphere. - **Afb. 34** Longitudinal cut of the brain. In the cerebrum, we become aware of the perceptions we make. Also, the impulses arise here to control muscles for conscious movements. The cerebellum plays an important role in maintaining your balance and coordinating your movements. Your perceptions are adjusted here to your movements. Often you perform multiple movements at the same time. The cerebellum coordinations all the movements of your body. For example, if you want to pick up something and you extend your arm, you use your senses (especially your eyes) to perceive all sorts of changes. In your cerebellum, these perceptions are combined with your movements. This allows you to be able to run, look around, and throw the ball into the basket at the right time while playing sports. ## BRAIN CENTERS The cerebral cortex in the cerebrum consists of areas with different functions. The function of a number of centers in the cerebral cortex is known (see Figure 35). - **Afb. 35** Exterior view of the brain with the location of the brain centers. You can distinguish between sensory centers and motor centers. Sensory centers receive impulses. The location in the cerebral cortex where these impulses arrive and are processed, determines the nature of the perceptions you make. In the visual cortex, for example, impulses arrive that originate from your eyes. Because the impulses in the visual cortex are processed, you see something and become aware of what you see. In motor centers, impulses arise for movements you consciously want to make. The location where the impulses arise, determines which skeletal muscles will move. A motor center for a certain body part is located close to the sensory center for that body part (also see BiNaS table 88C). Because the nerve tracks cross each other in the brainstem, the left cerebral hemisphere has sensory and motor centers for all the parts of the body on the right side of the body, and vice versa. Although the cerebral hemispheres are similar in construction, they do not have an identical function. For example, most people can recognize faces better with the right cerebral hemisphere and speech seems to come more from the left cerebral hemisphere. All parts of the body are connected to sensory centers. Most sensory centers lie together in the cerebral cortex. The sensory centers for smelling, hearing and seeing lie apart in the cerebral cortex. When impulses arrive in a primary sensory center, you become aware of the stimuli. In the secondary sensory centers (or association centers) the connection is made between the perception and previous perceptions. By associating information in your memory with the incoming stimuli, you are able to interpret and understand the stimuli. For example, if someone has a damage to the secondary auditory centers, they can still hear normally, but can not understand what they hear. Most of the motor centers lie together in the cerebral cortex. A motor center for a certain body part lies close to the sensory center for that body part. The motor centers for writing and speaking are located separately in the cerebral cortex. In the primary motor centers, impulses arise for movements that you consciously want to make. They are conducted via the brainstem and motor neurons to muscles in the head and neck, or via the spinal cord and motor neurons to muscles in the trunk and limbs. In the secondary motor centers, the impulses that come from the adjacent primary motor centers are coordinated. The secondary motor centers also receive information about the posture of (parts of) the body, so that the primary motor centers can control the right muscles. ## SPINAL CORD The spinal cord lies well protected in the vertebral canal, which is formed by the openings in the closely spaced vertebrae (see Figure 36). Around the spinal cord, there are three spinal meninges that provide protection. In the middle of the cord lies a cavity: the central canal. This canal is filled with fluid and is directly connected to the cerebrospinal fluid in the brain cavities. - **Afb. 36** Location of the spinal cord in the vertebral column. The spinal cord extends from the topmost cervical vertebra (the atlas) to the second lumbar vertebra. From the cervical vertebrae to the coccyx, spinal nerves exit the vertebral canal. They leave through openings on the left and right between the vertebrae to the outside and connect the spinal cord with the tissues and organs of the limbs and the trunk (see Figure 37). - **Afb. 37** Spinal nerves and cranial nerves. Spinal nerves are mixed nerves. On the back side, the axons of the sensory neurons come together in sensory nerves. The thickenings in these nerves are formed by a cluster of cell bodies from the sensory neurons called spinal ganglia (singular: spinal ganglion). The cell bodies in the ganglia are connected by axons to interneurons in the spinal cord. The axons of motor neurons come together on the abdominal side in motor nerves. A sensory nerve and a motor nerve come together in a spinal nerve. - **Afb. 38** Overview of the location of neurons in the spinal cord and in a spinal nerve (schematic).